1. Field of the Invention
The present invention relates to a photographic film cassette and more particularly to a photographic film cassette which has a plastic molded cassette shell and light-trapping members adhered to the upper and lower inner surfaces of the port portion of the cassette shell.
2. Description of the Related Art
Conventional 135-type (35 mm) photographic film cassettes have a cylindrical housing and a pair of end caps which are formed of a thin metal plate. Such a photographic film cassette has a film passage mouth formed in its port portion. In order to prevent ambient light from entering the film cassette through the film passage mouth and damaging photographic film contained therein, light-trapping members are adhered to the upper and lower inner surfaces of the port portion. Since the metal is heat resistant, the light-trapping members are adhered thereto by a hot-melt adhesive.
Self advancing type photographic film cassettes are also well known. U.S. Pat. Nos. 4,834,306 and 4,846,418 and Japanese Patent Laid-Open Publication No. 3-37645 all disclose film cassettes in which the leading end of a photographic film is initially located inside a cassette shell prior to use and advanced out of the cassette shell by rotation of the spool. In those film cassettes, the cassette shell is molded of a plastic material, or the like. In general, plastics are not highly resistant to heat. Therefore, it is preferable not to use a thermal adhesion method when attaching light-trapping members to such a cassette shell.
For this reason, a bonding method is utilized in which a heat-activated type adhesive layer, including metallic powder, is applied to the back surfaces of light-trapping members. The adhesive elements of the adhesive layer are activated by radio frequency induction heating so as to adhere the light trapping members to the cassette shell without damaging the same. Also, the use of an adhesive which has enough adhesive power at room temperature has been tried.
In the former, when cutting the light-trapping members from a web with the metallic powder into a predetermined size, metallic dust is yielded, which causes scratches of the film. In the latter, it is impossible to entirely prevent the adhesive from oozing out of the adhesive area. Further, if the adhesive is of the hygroscopic curing type, it is difficult to control moisture during handling of webs and thus the adhesive may not cure properly. If it is the anaerobic type or the ultraviolet curing type, complete elimination of air after adhesion or the efficient irradiation of ultraviolet rays, respectively, is also very difficult.